Uses of coordination compounds
1. Dyes and Pigments
Coordination compounds have been used from the earliest
times as dyes and pigments, for example
madder dye which is red, was used by the ancient Greeks and others. It is a complex of hydroxyanthraquinone. A more
modern example is the pigment copper phthalocyanine, which is
2. Analytical Chemistry
The coordination compounds used for various purpose, in
the laboratary are as follows.
a) Colour Tests :
Since many complexes are highly coloured they can be used as colourimetricreagents e.g. formation of red
2,2'-bipyridyl and 1,10-phenanthroline complexes
as a test for Fe2+
b) Gravimetric Analysis : Here chelating ligands are often used to form insoluble complexes e.g. Ni(DMG)2 and Al(oxine)3.
c) Complexometric Titrations and Masking Agents : An example of this is the use of EDTA in the volumetric determination of a wide variety of
metal ions in solution, e.g. Zn2+, Pb2+,Ca2+,Co2+,Ni2+,Cu2+, etc. By
careful adjustment of the pH and using
suitable indicators, mixtures of metals can be analysed, e.g. Bi3+ in the presence of Pb2+. Alternatively, EDTA may be used as
a masking agent to remove a metal ion
which would interfere with the analysis of a second metal ion present.
Sometimes certain metals can be
leached from their ores by formation of stable complexes e.g. Ag and Au as complexes of cyanide
Naturally occurring complexes include haemoglobin,
chlorophyll, vitamin B12 etc.
Therapeutic chelating agents are used as antidotes for
heavy metal poisoning. EDTA and other
complexing agents have been used to speed the elimination of harmful radioactive and other toxic elements from the
body. (e.g. Pb2+).
In these cases a soluble metal chelate is formed.
An example here is the use of
cis-Pt(NH3)2Cl2 as an anti-tumour drug.
Synthetic detergents containing chelating agents such as
tripolyphosphate. The chelating agent sequesters hard-water cations, rendering
them incapable of interfering with